Nozzle assembly for a jet propulsion engine



June 4, 1968 M. R. PIKE ET AL NOZZLE ASSEMBLY FOR A JET PROPULSION ENGINE Filed March 2, 1966 United States Patent 3,386,248 NOZZLE ASSEMBLY FOR A JET PRQPULSION ENGINE Malcom Roy Pike, Woodthorpe, Norman Arthur Kerridge, Alvaston, Derby, and Thomas Herbert Frost, Marston Montgomery, Derby, England, assignors to Rolls-Royce Limited, Derbyshire, England, a British company Filed Mar. 2, 1966, Ser. No. 531,144 Claims priority, application Great Britain, Mar. 26, 1965, 13,079/ 65 8 Claims. (Cl. 60-261) ABSTRACT OF THE DISCLOSURE A nozzle assembly for a jet propulsion engine comprises an axially movable shroud, a variable area convergent nozzle which is mounted within the shroud and which is axially fixed. There is provided a fixed divergent nozzle at the downstream end of the shroud and the shroud moves axially relative to the variable area final nozzle so that the fixed divergent nozzle may be placed both in an operative position in which it controls expansion of the jet gases leaving the variable area convergent nozzle and in an inoperative position in which it cannot exercise such control. The variable area convergent nozzle has a plurality of angularly spaced apart flaps each of which is mounted at its upstream end on a pivot and which have an axially extending curved portion. The curved portion is engaged by rollers carried by the shroud so that axial movement of the shroud effects radial movement of the flaps, the area of the convergent nozzle being increased when the shroud moves towards the operative position.

This invention concerns a nozzle assembly for a jet propulsion engine.

Accordingly to the present invention, there is provided a nozzle assembly for a jet propulsion engine comprising a convergent nozzle which is mounted within a shroud having a fixed divergent nozzle at its downstream end, and means for effecting relative axial movement between the shroud and the convergent nozzle so that the shroud may be placed both in an operative position in which it controls the expansion of jet gases leaving the convergent nozzle and in an inoperative position in which it does not exercise such control.

The convergent nozzle is preferably a variable area nozzle. Moreover, means are preferably provided for increasing the area of the convergent nozzle when the said relative axial movement has moved the shroud into or towards the said operative position.

Thus the convergent nozzle may be provided with a plurality of angularly spaced apart flaps each of which is mounted at its upstream end on a pivot and has an axially extending curved portion whose downstream end is spaced further from the pivot than the upstream end, each said curved portion being engaged by at least one roller carried by the shroud, whereby the said relative axial movement of the shroud efiects radial movement of the flaps.

Each curved portion is preferably engaged bet-ween two rollers carried by the shroud.

The external surface of the downstream end of the shroud may be radially inwardly curved to reduce drag.

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portion which extends downstream of the remainder thereof.

The invention also comprises a jet propulsion engine provided with a nozzle assembly as set forth above. Thus, the engine may have means for burning reheat fuel in the engine jet pipe; and the said annular space may, for example, be arranged to receive intake air.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which:

FIGURE 1 is a diagrammatic view, partly in section, of a jet propulsion by-pass turbine engine provided with a nozzle assembly according to the present invention,

FIGURE 2 is a broken-away sectional view showing part of the structure of FIGURE 1 on a larger scale,

FIGURE 3 is a broken-away sectional view taken on the line 3-3 of FIGURE 2, and

FIGURE 4 is a broken-away perspective view of the downstream end of the engine of FIGURE 1.

In FIGURE 1 there is shown a jet propulsion by-pass gas turbine engine 16 having in flow series an air intake 16, low and high pressure compressors 11, combustion equipment 12, and high and low pressure turbines 13. The jet gases leaving the downstream end of the turbines 13 are directed through a jet pipe 14 whose downstream end is provided with a convergent nozzle 15.

The engine 10 has an engine casing 16 between which and the jet pipe 14 there is provided an annular by-pass passage 17 which receives part of the air compressed by the low pressure compressor. The engine casing 16 is mounted within an outer casing 18 and spaced therefrom by an annular space 19 which, as will be seen from FIGURE 1, receives air which is spilled from the air intake 10. Alternatively, the annular space 19 could receive air from a separate air intake (not shown).

Mounted about the convergent nozzle 15, so as to be spaced therefrom by annular space 20, is an axially movable shroud 21. The shroud 21 is movable axially by means of a plurality (e.g. six) rams 22, each of the rams 22 being mounted on the outer casing 16.

The shroud 21 has a fixed divergent nozzle 23 at its downstream end. The shroud 21 is movable by the rams 22 between an operative or downstream position, shown in FIGURES 1 and 2, in which the fixed divergent nozzle 23 controls the expansion of the jet gases leaving the convergent nozzle 15, and an inoperative or upstream position (not shown) in which it does not exercise such control.

The convergent nozzle is axially fixed in position but is a variable area nozzle having a plurality of angularly spaced apart flaps 24 each of which is mounted at its upstream end on a pivot 25 mounted at the downstream end of the jet pipe 14. Each flap 24 has an axially extending curved portion 26 whose downstream end is spaced further from the pivot 25 than the upstream end thereof. The outer surface of each curved portion 26 is engaged by a roller 30 "which is rotatably mounted on a spindle 31, the spindle 31 extending between a pair of spaced arms 32 which are carried by a ring 33 mounted within the shroud 21, the ring 33 converting the stresses on the arms 32 into hoop stresses.

Secured to one of. the arms 32 is an arm 34 which carries a roller 35 which engages the inner surface of the curved portion 26. It will thus be appreciated that as the shroud 21 is moved axially between the operative and inoperative positions, the flaps 24 are moved radially, whereby the area of the convergent nozzle 15 is reduced as the shroud 21 is moved towards the inoperative position. As will be seen, the flaps 24 form a convergent nozzle in all positions of the shroud 21, the area of this convergent nozzle being varied as the shroud 21 is moved axially.

The shroud 21 has a downstream portion 36 which is radially inwardly curved to reduce drag and which has a 3 portion 37 which extends downstream of the remaining portion of the shroud 21.

The portion 37, which is disposed in a region which is shielded by the fuselage (not shown) where satisfactory inflow of air to the nozzle 23 is not possible, improves the supersonic flight performance.

The annular space 19 communicates with the annular space 20. The air spilled from the air intake is therefore supplied to the annular space so as to flow downstream therethrough, whereby to prevent the entry of jet gases into the annular space 20. The flow of jet gases through the convergent nozzle 15 will exercise an ejector effect upon the air flowing through the annular space 20.

The air from the air intake 10 which passes through the annular space 19 will also serve to ventilate the engine bay (not shown) in which the engine 10 is housed, and to cool the rams 22. Additionally, this air will help to prevent severe over-expansion and instability of the jet gases when the ratio of the pressure in the jet pipe 14 to ambient pressure is substantially less than is required for full expansion to the final area of the nozzle 23.

The shroud 21 may be shaped asymmetrically to suit particular flight conditions. Thus, the shape of the shroud may be such that during subsonic cruise conditions, the amount of air from the annular space 19 which mixes with the jet gases can be such as to reduce base drag.

Means (not shown) are provided for burning reheat fuel in the jet pipe 14.

When reheat is not employed, the shroud 21 may be placed in its inoperative position, and the engine 10 will then be provided with a convergent nozzle suitable for subsonic conditions.

When reheat is selected, the shroud 21 is moved downstream into its operative position, and as it is moved, the area of the nozzle 15 is correspondingly increased. The engine 10 thus becomes provided with a convergent-divergent nozzle suitable for supersonic flight. In this position the fixed divergent nozzle 23 enables a significant proportion of the thrust of the jet gases from the jet pipe 14 to be realised.

We claim:

1. A nozzle assembly for a jet propulsion engine comprising an axially movable shroud, a variable area convergent nozzle which is mounted within the shroud and which is in an axially fixed position, a fixed divergent nozzle at the downstream end of the shroud, and means for effecting axial movement of the shroud relative to the variable area convergent nozzle so that the shroud may be placed both in an operative position in which it controls the expansion of jet gases leaving the variable area convergent nozzle and in an inoperative position in which it cannot exercise such control, said variable area convergent nozzle being provided with a plurality of angularly spaced apart flaps each of which is mounted at its upstream end on a pivot and has an axially extending curved portion whose downstream end is spaced further from the pivot than the upstream end, each said curved portion being engaged by at least one roller carried by the shroud, whereby the axial movement of the shroud effects radial movement of the flaps, the area of the convergent nozzle being increased when the shroud moves towards the said operative position.

2. A nozzle assembly as claimed in claim 1 in which each curved portion is engaged between two rollers carried by the shroud.

3. A nozzle assembly as claimed in claim 1 in which the external surface of the downstream portion of the shroud is radially inwardly curved to reduce drag.

4. A nozzle assembly as claimed in claim 1 in which there is an annular space between the shroud and the convergent nozzle, means being provided for supplying gas to said annular space so as to flow downstream therethrough.

5. A nozzle assembly as claimed in claim 1 in which the shroud is asymmetrically shaped to suit predetermined flight conditions.

6. A nozzle assembly as claimed in claim 1 in which the shroud has a portion which extends downstream of the remainder thereof.

7. A jet propulsion engine provided with a nozzle assembly as claimed in claim 1, means being provided for burning reheat fuel in the engine jet pipe.

8. A jet propulsion engine provided with a nozzle as sembly as claimed in claim 4, the said annular space being arranged to receive intake air.

References Cited UNITED STATES PATENTS 2,794,317 6/1957 Brown 239-26539 2,974,480 3/1961 Kurti 239265.39 3,027,710 4/ 1962 Maytner 239265 .13 3,044,258 7/ 1962 Carlton 239265.39 3,049,873 8/1962 Weeks 239265.39 3,068,645 12/1962 Alford 239-26537 3,153,321 10/1964 Spears 239-265.39 3,157,027 11/1964 May 239265.41 3,161,019 12/1964 Keenan -264 MARTIN P. SCHWADRON, Primary Examiner. DOUGLAS HART, Examiner. 

